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/ 8                                GEOGRAPHICAL RANGE                           CHAP.
Altogether the enormous progress in the complexity of the
brain from the early Tertiary mammals down to the present, is ,
one of the most remarkable revelations of palaeontology. It
goes perhaps some way in explaining the remarkable diversity
in mode of life exhibited by the mammals as compared, for
example, with the birds, whose brains have not diverged so much
or in so many directions from the primitive form.
The present Distribution of the Mammalia.In the follow-
ing pages some of the principal facts in the geographical range
of the orders, families, arid many of the genera of Mammalia
will be given. It has been justly observed by Mr. Sclater
that the habitat of an animal is as much a part of its
definition as is its structure or external form, ISFo systematic
account of the Mammalia would therefore be complete without
such geographical facts. But that branch of zoology which
is concerned with the past and present distribution of animals
is wider in scope than this. Zoogeography deals not only
with the actual facts in the range of animals, but with the
inferences as to past changes in the relations of land and sea
which the facts seem to indicate, and with speculations as to
the place of origin of the different groups, of which more than
hints are sometimes given by their past and present distribution.
In addition to this, the earth can be mapped out into provinces
and regions which are definable by their animal inhabitants.
In the present volume, dealing only with the Mammalia, it will
be obviously impossible to enter fully into the entire subject
of zoogeography. All that will be attempted is a brief general
survey of the science so far as it can be illustrated by the
Mammalia. For fuller knowledge the reader is referred to the
treatises mentioned below.1
There are certain facts in the distribution of animals which
are commonplaces of knowledge, but which may be set forth
with definiteness. Everybody knows that an animal has a given
range: Elephants, for example, are found in India and certain
adjacent parts of Asia, and again in Africa; the Rhinoceroses
have roughly the,same range; the Tiger is limited to Asia-; the
1 "Wallace, The Geographical Distribution of Animals, 1876. Heilprin, The
Distribution of Animals, Internal Scientific Series, 1887. Beddard, A Teafft-Qook
of Zoogeography, Cambridge Katural Science Manmals, 1895, Lydekker, &eogrcvpM~
col BX&tory of Mammals, Cambridge Geographical Series, 1890.* W. I*, and P. I.
Sclater, The &eogrtqphy of Mammals, Kegan Paul and Co* 1809.